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Soil Science

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Browsing Soil Science by Subject "Carbon sequestration."

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    Analysis of global gully characteristics and the impacts of gabions and grass on sediments and carbon storage.
    (2018) Dube, Hastings Bangani.; Muchaonyerwa, Pardon.; Chaplot, Vincent A. M.
    Abstract available in PDF file.
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    Assessing water use effeciency and carbon sequestration potential of different wheat (Triticum aestivum) genotypes.
    (2019) Mbava, Nozibusiso Odette.; Zengeni, Rebecca.
    Poor soil fertility status and limited water availability have been identified as two of the major constraints to crop production in South Africa. Under these conditions, growing crop genotypes that will sequester more carbon into the soil and be more water use efficient is crucial to improve crop production thus alleviate food insecurity. The aim of the study was to assess water use efficiency and carbon sequestration potential of different wheat genotypes. The experiment was set up under field and greenhouse conditions using 100 wheat genotypes from CIMMYT. These were grown at 25% (water-stressed) and 75% (non-stressed) field capacity (FC) using an alpha lattice with 10 blocks and 10 genotypes per block. Treatments were replicated twice in the field and three times in the glasshouse. After harvest the 10 best wheat genotypes were separated into roots and shoots, their chemical composition was analysed prior to the incubation experiment. About 0.25 g each of wheat root (RT) or shoot (ST) of the selected wheat genotypes were thoroughly mixed with 100 g of soil then transferred into an air tight PVC pot. NaOH solution was also placed inside the incubation pot to trap CO2 released during decomposition, and this was measured on day 0, 7, 15, 23, 31, 39, 47, 55, 63, 77, 91,105, and 120 of incubation. The results from the field and glasshouse experiments showed that average wheat grain yield (GY) varied from 326 g m-2 to 2062 g m-2, shoot biomass (SB) ranged from 1873 g m-2 to 3726 g m-2 while total plant biomass (PB) ranged from 2992 g m-2 to 6289 g m-2. Grain carbon stocks (GCS) averaged 132 g C m-2 and 167 g C m-2 in the glasshouse under stressed and non-stressed conditions, respectively. The total plant carbon stocks (PCS) ranged from 691 g m-2 to 3093 g m-2 (i.e. 348% difference) in the glasshouse, while they ranged from 835 g m-2 to 4016 g m-2 (i.e. 381% difference) in the field. Water use efficiency for grain yield production (WUE-GY) ranged from 0.12 g m-2 mm-1 to 2.10 g m-2 mm-1 (i.e. 18 fold increase) in the glasshouse under stressed conditions while it was 0.57 g m-2 mm-1 to 4.01 g m-2 mm-1 in the field under stressed conditions. WUE components varied amongst wheat genotypes. LM75 exhibited higher WUE-GY under stressed conditions while genotypes LM48 and LM47 exhibited lower WUE-GY under non-stressed conditions. LM75 was also ranked the best genotype for WUE-PCS while BW162 was ranked the best genotype for WUE-RCS. In the incubation experiment the shoot treatments evolved higher net CO2-C compared to root treatments. Net CO2-C was highest within the first two weeks and declined with time. Amongst the root treatments, BW140 RT evolved the highest net CO2-C (86.6 mg CO2-C kg-1 soil), while LM70 RT evolved the lowest (48.8 mg CO2-C kg-1 soil). In shoot treatments BW162 ST and BW140 ST evolved the highest net CO2-C with average values of 218.7 and 223.8 mg CO2-C kg-1 soil respectively. Comparing all the 10 treatments LM70 RT evolved the lowest while BW140 ST and BW162 ST had the highest net CO2-C. The findings revealed that variability in storing C under different scenarios of water availability exists among the wheat genotypes studied. Also, the residues of different wheat residues exhibit potential of sequestering more C into the soil thus improve soil fertility.
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    Grassland degradation and rehabilitation of soil organic carbon and nitrogen stocks.
    (2014) Dlamini, Phesheya.; Chaplot, Vincent A. M.; Chivenge, Pauline.
    Land degradation is widely considered to adversely affect soil fertility, soil quality, constrain productivity, subsequently leading to a decline in soil organic carbon (SOC) and nutrients in soils, yet little is known about the stocks, environmental controls, destabilization mechanisms and carbon sequestration potential of degraded grassland soils. The aim of this dissertation was to evaluate (1) the impact of land degradation on SOC and nitrogen (N) stocks, distribution and SOC quality, to elucidate the environmental controls, in a communal rangeland with varying intensities of degradation, (2) to examine the rehabilitation potential of the same rangeland (3) to assess the spatial variability and replenishment potential of SOC and N stocks in a typically degraded grassland catchment. A meta-analysis was conducted to provide a quantitative review of the impact of land degradation on SOC stocks in grassland soils, worldwide. Subsequently, the impact of degradation on SOC and N stocks and organic matter quality was investigated in a communal rangeland in the KwaZulu-Natal province, South Africa with varying intensities of degradation. Thereafter, different rehabilitation techniques were applied in the same communal rangeland to replenish SOC and N stocks. Advantage was also taken of 23 ha degraded grassland catchment to assess the spatial variability, carbon replenishment potential of SOC and N and to elucidate the main environmental controls. Degradation resulted in a significant depletion of SOC stocks in grassland soils, both in the meta-analysis and field experiment. The meta-analysis indicated that the depletion of SOC stocks as a result of degradation was more pronounced in sandy acidic soils under dry climate than clayey soils under wet climate. The field experiment showed that degradation significantly depleted SOC stocks by 89% and N stocks by 76% in sandy acidic soils at the study site. The reduction of the stocks due to degradation was accompanied by an increase in soil bulk density, a decrease in soil aggregate stability and concomitant decrease of macro and micronutrients (e.g, Ca by 67%; Mn, 77%; Cu, 66% and Zn, 82%). SOC and N stocks decreased sigmodially with a linear decrease in grass aerial cover. After two years, the “Savory and fertilization techniques increased SOC stocks by 6.5% and 3.9%, respectively. At catchment level, degradation led to high spatial variability of SOC and N stocks controlled primarily by soil surface characteristics, including grass cover, soil surface crusting and secondarily by topography. The carbon replenishment potential of degraded grassland catchment was estimated to be 4.6 t C ha-1, with clay-rich Acrisols having a greater capacity to replenish SOC stocks than sandy Luvisols and Gleysols. In conclusion, the results of this dissertation indicate that degradation results in high depletion of SOC and N stocks. However, rehabilitation has the potential for carbon sequestration and can lead to more sustainable grassland ecosystems.